The prior art discloses numerous paint delivery and application systems including systems using pigging technology. Such systems may be used to apply seriatim paints of different colors, for example, to a plurality of substrates, such as vehicle bodies on a moving conveyor in a paint spray booth. The term “paint,” as used herein, includes solvent or water base paints used to paint or coat a substrate and generically any coating, including protective coatings, which may be applied to a substrate using an applicator, such as a sprayer or rotary atomizer. Depending on its function in the coating delivery system, pigs or pigging elements are variously referred to in the prior art as shuttles, separating elements, terminating pistons, plugs, etc. Generally, a pig or pigging element is utilized in the prior art paint delivery systems to push paint either toward the applicator to apply the paint, separate different paints or solvent, scrape or clean the paint supply lines or push paint in the supply line back to the paint supply switching device or color changer. Pigs or pigging elements have also been used to separate fluids in a delivery line including paints of different colors, solvents, etc. which may be driven through the delivery line by pneumatic pressure or other fluid.
A conventional paint supply and application system includes a source of paint under pressure, an applicator, such as a rotary atomizer, generally at high voltage, sprayer or the like, a source of solvent under pressure, and a supply line connecting the source of paint and solvent to the applicator. Where the source of paint and solvent includes a color changer or paint supply switching device, the paint supply and application system may also include a paint canister which may be mounted on a robot, for example, and the color changer is generally at ground potential. When a second paint is to be applied, the canister may be switched for a canister filled with a different paint or the canister may be connected to a source of a different paint. As used herein, the term “canister” or “paint canister” includes any container suitable for receipt and delivery of paint.
A paint delivery and application system using pigging technology for application of different paints, as disclosed in the prior art, includes a color changer or paint supply switching device, including sources of different paints and solvent under pressure, a paint applicator, a supply line connecting the color changer and the applicator and a pigging element or pig which is received in the supply line to push paint through the supply line either toward the paint applicator to apply paint to a substrate or from adjacent the paint applicator to the color changer to recover paint in the supply line. As the pigging element moves through the supply line, it pushes paint or solvent through the supply line and cleans or scrapes paint or solvent from the supply line. In one embodiment disclosed in the prior art, a pigging element is inserted into the supply line to push paint from a color changer to the applicator and the pigging element is then removed. In another embodiment disclosed in the prior art, the supply line between the paint supply switching device and the applicator includes two pig receiver stations, including a first station adjacent the paint supply switching device or color changer and a second pig station adjacent the paint applicator. The pig receiver stations are defined by a chamber which permits paint or solvent to flow around the pigging element. The pigging element is releasably retained in the first receiver station by a clamping means and then released to push paint from the first pig receiver station adjacent the paint applicator to push paint in the supply line to the paint applicator. The pigging element is then driven back under pneumatic pressure to the first receiving station to push paint in the supply line back to the paint supply and switching device or color changer to recover paint in the supply line.
There are several problems associated with the prior paint delivery and application systems described above, particularly in mass production applications, wherein the part to be painted is generally supplied to the applicator in a paint spray booth by a conveyor requiring a short cycle time. As will be understood by those skilled in this art, the longer the cycle time, that is the time required to change from a first paint to a second paint, the greater the expense. At present, the cycle time of a conventional paint supply and application system is at least about 30 seconds. To accommodate this cycle time, the manufacturer can either slow the conveyor through the paint booth or add additional paint application equipment. It would therefore be desirable to reduce the cycle time which is one object of this invention.
Another problem is associated with the electrical or electrostatic charge applied to the electrically conductive paint by the paint applicator during application, particularly with rotary electrostatic paint atomizers of the type commonly used in mass production applications. In a typical application, the color changer is at ground potential and thus the electrically charged paint applicator must be electrically isolated from the color changer during application of paint. This presents a particular problem when attempting to reduce cycle time. Other problems with conventional paint supply and application systems include waste of paint, cycle time for cleaning and flushing of the paint applicator and paint lines and changing of paint colors, particularly including but not limited to robotic paint systems.
Other problems associated with paint delivery and application systems of the type described herein, particularly for mass production applications, including automotive applications, generally relate to the precise metering of liquid coating or paint applied to the part because of differences in the temperature and viscosity of the liquid coating and different parts may be painted in the same line. Where paint canisters are utilized, it would also be desirable to use a nonconductive cylinder which does not expand or contract under varying conditions. In certain applications, for example, it would be desirable to provide an excess of available paint to compensate for variations in temperature and viscosity and return the excess paint to the color changer.
The paint delivery and application systems and methods of this invention solve the above-identified problems, including reduced cycle time, automatic switching of paint and rapid flushing of the paint applicator between applications and electrically isolates the color changer from the applicator permitting use of electrically conductive paint, including but not limited to water based paints. The paint delivery and application systems of this invention also eliminates waste of paint. The paint delivery and application systems and method of this invention is also easily adapted for robotic paint application systems using a rotary atomizer and applying electrically conductive paint.